Coated composite metal part

ABSTRACT

A COATED COMPOSITE METAL PART COMPRISED OF TWO OR MORE METALLIC COMPONENTS EACH HAVING A FUSED-ON CERMET PROTECTIVE COATING AND A METALLIC WELD AREA JOINING THE COMPONENTS IS PROVIDED WITH A NOVEL FLAME-SPRAYED PROTECTIVE COATING OVER PORTIONS OF THE FUSED-ON CERMET COATING AND OVER THE ADJOINING WELD AREA TO DEVELOP IMPROVED METAL PART RESISTANCE TO SURFACE CORROSION ATTACK.

United States Patent Oflice 3,794,514 COATED COMPOSITE METAL PART HaroldJ. Michael, Columbus, Ohio, assignor to Rockwell InternationalCorporation No Drawing. Original application Nov. 27, 1970, Ser. No.93,493, now Patent No. 3,702,770, dated Nov. 14, 1972. Divided and thisapplication Mar. 3, 1972, Ser.

Int. Cl. C23c 7/00 U.S. Cl. 117--46 FS 4 Claims ABSTRACT OF THEDISCLOSURE CROSS-REFERENCE This is a division of application Ser. No.93,493, filed Nov. 27, 1970 and now issued as U.S. Letters Patent No.3,702,770, issued Nov. 14, 1972.

SUMMARY OF THE INVENTION Aluminum metal powder is mixed in prescribedproportions with a finely divided alkali titanate compound, such aslithium-silico-titanate (lithium titanium silicate), lithium titanate,or both, by way of example, for subsequent application to any of anumber of different metal parts using conventional oxy-acetylene flamespray equipment or plasma arc equipment to thereby develop improvedmetal part resistance to surface corrosion. The specified compositionsare suitable for application in the same manner over metal part Weldareas, including application over weld areas that join metal partspreviously coated with different but compatible types of fused-onceramic-metallic protective coatings.

DETAILED DESCRIPTION The following general formulation identifies theprincipal constituents, by range and on a 100 parts by weight basis, ofthe ceramic-metallic protective coating compositions of this invention.

Coating compositions Constituent: Range Aluminum metal powder, -120 +325mesh,

spherical particles 20-80 Alkali titanate compound, 120 +325 mesh frit20-80 Total 100.0

Aluminum powder constituent The ceramic-metallic composition of thisinvention utilizes l20 mesh +325 mesh aluminum powder such as 3,794,514Patented Feb. 26, 1974 is commonly purchased commercially in a spraygrade form, such metal powder having particles which are substantiallyspherical in configuration.

Alkali titanate compound constituent One preferred alkali titanatecompound constituent is lithium-silico-titanate, sometimes referred toherein as lithium titanium silicate, and essentially non-homogeneousopalescent glass having two distict compositional phases in both theliquid condition and the solid condition. Such constituent is preferablycompounded to have a 1:1:1 molecular ratio of Li O to SiO to TiO and maybe made in the following manner.

The Example I ingredients given below, stated on a parts total weightbasis, are combined by thorough dry blending, smelted at 2000 F.2300 F.,and fritted to form the preferred lithium-silico-titanate compoundconstituent.

EXAMPLE I.CONSTITUENT COMPOSITION Preferred Range amount Component:

Silica (S102) 20. 0-80. 0 28. 2 Titania (TiOz) 20. 0-80. 0 37. 3 LithiumCarbonate (LlzCO3) 12. 4-74. 0 34. 5

Total 100. 0 100. 0

Preferred Range amount Total 100. 0 100. 0

Another alkali titanate compound constituent satisfactory for practiceof this invention is lithium titanate. Such may be included in thecompositions of this invention optionally or additionally with respectto lithium-silicotitanate, for example. It provided by way of addition,the compound functions to further decrease the electrical surfaceresistivity property of the final coating to thereby develop improvedanodic protection for the resulting coated metal part. The belowdetailed lithium titanate constituent, however, does not in most casesalone provide optimum surface wetting during application of thecomposition to metal parts by flame spraying. Such lithium titanateconstituent is compounded to have a preferred 1:1 molecular ratio of TiOto U 0 and may be made from the following Example II ingredients,detailed on a 100 parts total weight basis.

EXAMPLE II Constituent composition Preferred Component: amount Lithiumcarbonate (Li CO 48.1 Titania (T102) 51.9

Total 100.0

The ingredients of the constituent are combined by thorough blending(either wet or dry) and fused into clinker form in an air furnace at atemperature of approximately 2000 F.i50 F. for subsequent crushing andscreening. The above Example II ingredients may alternatively be meltedat a temperature of approximately 2300 Fri-50 F. and fritted in lieu ofbeing fused into clinker form for the subsequent processing.

The resulting ground clinker or frit is graded to pass a No. 120 US.standard sieve and remain on a No. 325 US. standard sieve for use. As inthe case of the lithium titanium silicate constituent, particles largerthan 120 mesh may be further ground for use; particles of a 325 meshsize may be re-charged into subsequent lithium titanate constituentbatches as cullet for re-firing.

It should be noted that other alkali titanates may be used in thecoating composition formulations although lithium titanate compounds arepreferred inasmuch as lithium is more electro-positive and providessuperior anodic protection in comparison to other alkali metal titanatessuch as sodium titanate or potassium titanate or in comparison to alkaliearth metal titanates such as the titanates of magnesium, calcium,strontium, or barium. Stated in another manner, lithium titanatecompounds appear to particularly enhance or improve the electricalsurface conductivity of the applied coating.

The following Example III, Example IV, and Example V coating compositionformulations, given on a 100 parts by total weight basis, are examplesof embodiments of this invention that have been utilized forsatisfactorily developing improved resistance to corrosion attack formetal parts to which the composition has been applied.

EXAMPLE III Coating composition Preferred Constitutent: amount Aluminummetal powder, 120 +325 mesh spherical particles 40Lithium-silico-titanate, 120 +325 mesh frit 40 Lithium titanate Li TiO120 +325 mesh frit Total 100 EXAMPLE IV Coating composition PreferredConstitutent: amount Aluminum metal powder, 120 +325 mesh sphericalparticles 50 Lithium-silico-titanate, 120 +325 mesh frit 50 Total 100EXAMPLE V Coating composition Preferred Constitutent: amount Aluminummetal powder, -l20 +325 mesh spherical particles 50 Lithium titanate (LiTiO -120 +325 frit 50 Total 100 Details with respect to application ofany of the above Examples III through V coating compositions to metalparts by flame spraying are given below.

The desired constituents of 120 +325 mesh screen size for a particularcoating composition prior to application of the composition to a metalpart by flame spraying are first carefully weighed to the properproportions and then dry blended until a uniform color is obtained.Flame spraying, as suggested previously, is then accomplished usingeither conventional oxy-acetylene flame spray equipment or conventionalplasma arc fiame spraying equipment depending upon availability. Ineither case, however, it is necessary that the metal part, which may bea large milled steel structural part by way of example, should becleaned by mechanical means in those areas which are to be coated.Cleaning may be accomplished either by abrasive blasting using a 40-80mash clean sand or Alundum grit, by disc sanding, or by stiif wirebrushing. The areas to be coated basically must be free of oxide, scale,welding flux, and other foreign material prior to application of thecoating composition. Since roughened, clean metal surface is essentialto good adherence, any loose particles should therefore be removed fromthe metal part surface as by blowing using clean, dry, compressed air.

Using conventional oxy-acetylene flame spray equipment, by way ofexample a Metco powder spray gun with a ceramic material feed nozzlehaving a No. 2 feed orifice, the compositions are applied by box orcross coating the metal part practicing the following steps. First, andprior to starting the flow of composition through the gun, preheat thesurface to be initially sprayed by passing the gun flame over thesurface at a distance of from 6" to 8" thereby accomplishing a degree ofpre-heating. Next, composition flow is started, adopting the equipmentmanufacturers control setting recommendations as to feed setting, oxygenflow, and acetylene flow, and application is accomplished by sprayingthe metal part surface using horizontal straight-line rather thanarc-type motion with the composition material impinging upon the metalpart surface at as near a angle as possible. After the pre-heating hasbeen accomplished with respect to the area to be initially coated, theremainder of the metal part is normally automatically pre-heated as thespraying work progresses. Adequate coverage of the metal part is usuallyobtained using one cross or box coat with a composition deposit densityof from 20 to 23 grams of composition per square foot of metal partsurface. Care must be taken that the speed of application is not so fastas to produce a loose, powdery-type coating. Normally non-porous coatingis obtained with gun travel over the work at a velocity of not more thanfour feet per minute.

The non-porous composition coating as sprayed has excellent bond inadhesion as well as cohesion. The coating composition as sprayedprovides excellent long time anodic protection for numerous differentferrous metals, stainless steels, and nickel-base alloys exposed to saltcorrosion environments. In some cases (Example I, Example IIIformulations) the applied intermetallic compound coating has essentiallya zero resistance to electrical current flow with as little as 40% to50% by weight aluminum metal content. In addition, the coating hasoutstanding resistance to impact, bending, or deformation failure byvirtue of a high degree of inherent ductility. The coating is compatiblewith fused-on type of cermet protective coatings, such as the coatingsdetailed in my co-pending application for US. Letters Patent Ser. No.69,914, filed Sept. 4, 1970, and assigned to the assignee of thisapplication, now US. Letters Patent No. 3,706,579, granted Dec. 19,1972, and has also been successfully applied over conventional weldsthat serve to join two metal parts previously coated with such fused-0ntype of cermet protective coatings.

Specifically, the invention involved a metal part comprised of twocomponents having one such fused-on cermet protective coating applied tometallic exterior surface areas thereof and of a weld area joining saidpart component surface areas together, said weld area having aprotective coating adhered thereto consisting, on a parts total weightbasis, of the product at an elevated temperature of approximately: (a)20 to 80 parts aluminum metal powder in finely divided sphericalparticle form mixed with (b) 20 to 80 parts of alkali titanate compoundin finely divided frit form, said alkali titanate compound beingselected from the group consisting of lithium titanate andlithium-silico-titanate.

What is claimed is:

1. A metal part comprised of at least two metallic components, eachhaving a fused-on cermet protective coating applied to the surface areasthereof, a weld area joining said components and flame-sprayed over saidweld area a protective coating consisting of:

(a) to 80 parts by weight aluminum metal powder in finely dividedparticle form mixed with (b) 20 to 80 parts by weight of alkali titanatecompound in finely divided frit form, said alkali titanate compoundbeing selected from the group consisting of lithium titanate,lithium-silico-titanate and mixtures thereof.

2. The invention defined by claim 1 wherein said weld area protectivecoating consists of approximately parts by weight of aluminum metalpowder, 40 parts by weight of lithium-silico-titanate, and 20 parts byweight of lithium titanate.

3. The invention defined by claim 1 wherein said weld area protectivecoating consists of approximately parts References Cited UNITED STATESPATENTS 3,607,343 9/1971 Longo et al. 117-105.2 2,904,449 9/1959Bradstreet 117-105.2 3,667,985 6/1972 Levine et a1. 11722 3,721,5773/1973 Wocrner 117-106 ALFRED L. LEAVITT, Primary Examiner J. W. MASSIE,Assistant Examiner US. Cl. X.R.

